Method for controlling exhaust gas recirculation valve

ABSTRACT

When an open-close valve does not operate despite a full (100%) continuous power feeding to a driving motor for an exhaust gas recirculation valve provided in an exhaust gas recirculation system, the power feeding to the motor is stopped to prevent previously the occurrence of a seizure of the motor.

TECHNICAL FIELD

This invention relates to a method of controlling an exhaust gasrecirculation valve (hereinafter referred to as an EGR valve) disposedin an exhaust gas recirculation system.

BACKGROUND ART

FIG. 1 is a conventional schematic diagram showing an arrangement of acontrol valve 11 as an EGR valve disposed in an exhaust gasrecirculation passage c which communicates an exhaust passage “a” of anengine E with an intake passage b.

The method of controlling the EGR valve involves driving and controllinga stepping motor M of a hybrid PM type 4-phase construction or the likeby an engine control unit (hereinafter referred to as ECU) 51, andcontrolling the opening and closing of the control valve 11 by thisstepping motor M. An open-loop control of the stepping motor M by astepping angle contributes to control over the degree of the opening ofthe control valve 11.

Such a control method using this kind of stepping motor M imposesrestrictions on the control over the degree of the opening of thecontrol valve 11 because the degree of the opening of the control valve11 can be controlled only by the stepping angle of the stepping motor M.The control valve 11 has a limited resolution for the controllableopening. In addition, the stepping motor M has a limited open-loopcontrol response characteristic due to the possible occurrence of astepping-out phenomenon. Once the stepping-out has occurred, thereliability falls as an error is still contained uncompensated in thecontrol amount.

To this end, the conventional control method of an EGR valve involvesgiving a predetermined return torque to the control valve 11 in thecontrol valve closing direction and, by a unidirectional driving of adirect current (DC) motor M (hereinafter referred to as a motor M),giving a motor torque to vary the control valve 11 in the openingdirection, and opening and closing the control valve 11 by the balanceof these torque.

An arrangement is described in Japanese Published Patent Feeding No.159405/1999. This arrangement includes an open loop control system forcontrolling an open loop of the motor M such that a motor torque isgenerated in correspondence with the target opening and closing positionof the above control valve 11; and a feedback control system forfeedback-controlling the motor M based on a deviation between input datacorresponding to the target opening and closing position of the abovecontrol valve 11 and detected data of the current opening and closingposition of the control valve 11.

FIG. 2 is a characteristic diagram showing the relationship between amotor torque and an opening and closing position of a control valve inan EGR valve of torque balance drive system.

First, the driving system using this motor M will be described. In casethe degree of the opening of the control valve 11 is feedback-controlledby the motor M, the generated torque of the motor M is continuouslycontrolled by feeding back the degree of the opening of the controlvalve 11 through unintermitted detection with a position sensor such asa sliding resistor type. Theoretically, the continuous control over thegenerated torque of the motor M promotes infinite reduction of theresolution of the controllable opening of the control valve 11.

This kind of method of controlling the EGR valve using the motor Madopted a so-called torque balance method. The method involves giving apredetermined return torque in the closing direction by means of aspring as urging means, giving a motor torque variable in the openingdirection by driving the motor M in the opening direction, anddetermining the valve opening position by the balance of these torque.

In case this kind of control method is adopted, since the EGR valve isconstantly given the return torque, the opening and closing positions(shift amount) vary in correspondence with the inclination of lines A, Bhaving a hysteresis characteristics due to friction as shown in FIG. 2.

Here, line A indicates an operating characteristic when the controlvalve 11 is opened by increasing the motor torque, and line B anoperating characteristic when the control valve 11 is closed by reducingthe motor torque. The inclination of the operating characteristics A, Bvaries depending on the spring constant of the spring to give the returntorque, and the operating characteristics A, B shift to the right orleft in FIG. 2 depending on the magnitude of the set torque.

Now, in order to control the control valve 11 having this kind ofoperating characteristics, suppose that a method is admitted, in whichthe motor is under the control of a P(proportional) I(integral) controlbased on a deviation between the input data corresponding to the targetopening and closing position of the control valve 11 and the detecteddata of the current opening and closing position of the control valve.In this case, owing to the relation of the operating characteristics A,B as shown in FIG. 2, it becomes difficult to stabilize the controlvalve 11 at the target opening position.

In other words, in order to open the control valve 11 to the targetopening position by increasing the motor torque, the P gain and the Igain must be increased to take control along the operatingcharacteristic A shown in FIG. 2. However, when the motor torque isincreased by the PI control under the control of this kind, thedeviation of the opening position of the control valve becomes “0” assoon as the control valve 11 is opened to the target opening position.The P component thus becomes “0” and the I component is cleared, withthe result that the control valve 11 begins to close by the returntorque.

FIG. 3 is a characteristic diagram showing the relationship between thetime and the operating position of a motor shaft.

At an initial stage in which the control valve 11 begins to close (atthe time the deviation is small), the P and I components are both smalland therefore the motor torque cannot overwhelm the return torque, withthe result that the deviation becomes large. Thereafter, even if thedeviation becomes large to a certain degree, the motor torque and thereturn torque balance with each other, the closing operation of thecontrol valve 11 cannot stop abruptly due to the inertia of the motor M.The control valve 11 thus cannot be opened immediately. If the gain ismade large such that a relatively large motor torque is generated evenat the time the deviation is small, there will be a vicious cycle thatincurs an increase of the overshooting and undershooting as shown inFIG. 3.

FIG. 4 is a longitudinal sectional view of the EGR valve.

The arrangement implementing a method of controlling the control valve11 in a so-called torque balance drive system using the motor M will nowbe described, with due consideration of the above circumstance.

Referring to FIG. 4, reference numeral 1 denotes a valve body havingtherein a passage forming a part of an exhaust gas recirculation passagec which is interposed in a recirculation system of the exhaust gas. Byupwardly moving the control valve 11 to contact it with a valve seat 12as shown in FIGS. 4 to 6 the exhaust gas recirculation passage c isclosed. Conversely, by downwardly moving the control valve 11 to departit from the valve seat 12 the exhaust gas recirculation passage c isopened.

Reference numeral 2 denotes a motor case for housing therein the motorM. Inside this motor case 2, reference numeral 21 denotes a rotor aroundwhich a coil 22 is wound, and reference numeral 23 a yoke with a magnet24. The lower end of the rotor 21 is rotatably supported on the valvebody 1 by a bearing 27.

Inside the rotor 21, a motor shaft 31 is screwed. The motor shaft 31 isprevented from rotating by a guide bush 13 in the body 1. It thereforefollows that the motor shaft 31 moves in the upward and downwarddirection depending on the amount of rotation of the rotor 21. A valveshaft 14 is held in contact with the lower end of the motor shaft 31,and an intermediate portion of which is guided by a guide seal 15 and aguide plate 16 so as to be movable in the upward and downward directionrelative to the valve body 1. The control valve 11 is attached to thelower end of the valve shaft 14.

Reference numeral 17 denotes a guide seal cover. Between a spring sheet18 mounted on the upper end of the valve shaft 14 and the guide plate16, a return spring 19 is interposed for urging the valve shaft 14 inthe upward direction, i.e., in the closing direction to urge the controlvalve 11.

The control valve 11 thus constituted is driven by the torque balancesystem as described above. In other words, the control valve 11 is givena predetermined return torque by the return spring 19 as urging means inthe control valve closing direction and is also given a variable motortorque in the control valve opening direction by driving the motor M. Bythe balance of these torque, the control valve 11 is opened and closed.

FIG. 5 is a block diagram of an ECU apparatus for carrying out themethod of controlling the EGR valve in the so-called torque balancedriving system using a motor.

Referring to FIG. 5 reference numeral 50 denotes a microcomputer as acontrol part for determining the motor driving voltage, and referencenumeral 52 a battery. Reference numeral 53 denotes a motor drivingvoltage converting part for converting the output of the control part 50to supply the converted output to the motor M, which includes a Zenordiode 53 a; a diode 53 b for passing a unidirectional current only tothe motor M; a field-effect transistor (FET) 53 c; and an interface 53 ddisposed between the control part 50 and the FET 53 c. Reference numeral56 denotes a regulator for generating a driving voltage (5V) of thecontrol part 50.

The control part 50 receives as inputs through interfaces 58, 59,respectively, a detected signal from an operating property sensor 57mounted on each part of the vehicle such as a crank angle sensor or thelike, as well as a detected signal from the position sensor 40. Theposition sensor 40 in this example is provided with a movable contactpart 42 movable on a resistor 41 to which a constant voltage (5V) isapplied from a voltage supply part 60. With the movement of the movablecontact part 42 as a result of the rotation of the rotor 21, a voltagecorresponding to the rotating position of the rotary shaft 31 isoutputted, as a detected signal, from the movable contact part 42.

Further, the above motor driving voltage converting part 53 switches onand off the voltage to be applied to the motor Mat a constant cycle. Bya pulse-width modulation (PWM) signal whose pulse width is determineddepending on the ratio of the on-time and the off-time per a cycle(driving duty), the FET 53 c is switched to control an average drivingvoltage to be applied to the motor M.

FIG. 6 is a block diagram showing a control part in the ECU.

Referring to FIG. 6, reference numeral 61 denotes a target positioncomputing part for computing an optimum opening and closing position ofthe control valve 11 based on the detected signal of the operatingproperty sensor 57, which outputs a voltage corresponding to the targetposition (hereinafter referred to as a “target value”). Referencenumeral 62 denotes an analog-digital (A/D) converter for performing anA/D conversion of a detected signal of the position sensor. 40, whichoutputs a voltage corresponding to the current position (hereinafterreferred to as a “current value”). Reference numeral 71 denotes anadder-subtractor for adding or subtracting the target value and thecurrent value. Reference numeral 63 denotes a PI controlled variablecomputing part for computing and outputting the PI controlled variable(voltage) by combining the proportional component (P component) and theintegral component (I component) based on the deviation between thetarget value and the current value. Reference numeral 64 denotes adriving duty computing part for computing the duty to be supplied to themotor M based on the output of the PI controlled variable computing part63.

Then, the operation of the control part will be described.

When a target value is given from outside, the current value detected bythe position sensor 40 and the above target value are added orsubtracted by the adding-subtracting part 71 to obtain a deviation. ThePI controlled variable computing part 63 computes a PI controlledvariable from the obtained deviation and outputs the computed PIcontrolled variable to the driving duty computing part 64. The drivingduty computing part 64 computes the driving duty based on the PIcontrolled variable and outputs the computed driving variable to themotor M.

Such a conventional method of controlling the EGR valve, in case thevalve shaft ceases to move due to biting, clogging of dirt, or the like,also ceases to move the motor shaft which is in abutment with the valveshaft. As a result, the motor extraordinarily generates heat caused bythe applied electric current and is in a danger of a seizure. Theconventional method of controlling the EGR valve cannot be quickly andappropriately deals with this kind of accident.

The invention has been made to solve the above and other problems and anobject thereof is to provide a method of controlling an EGR valve whichis able to prevent previously the occurrence of a seizure in the eventthe valve shaft has ceased to move.

DISCLOSURE OF INVENTION

A method of controlling an EGR valve according to the invention in whicha valve-open position is controlled by a torque balance between a returntorque given by urging means in the valve closing direction and a motortorque given by a motor in the valve opening direction, comprises thestep of stopping power feeding to the motor if an open close valvefailed to operate despite a full (100%) continuous power feeding to themotor for a predetermined period of time or more.

Therefore, even if a valve shaft ceases to move due to biting, cloggingof dirt, or the like, the occurrence of a seizure of the motor can beprevented previously.

In the method of controlling an exhaust gas recirculation valveaccording to the invention further comprises the step of driving themotor in the valve closing direction and thereafter driving the motor inthe valve opening direction again if the open-close valve failed tooperate despite a full (100%) continuous power feeding to the motor fora predetermined period of time or more.

Therefore, even in case the valve shaft ceases to move due to biting,clogging of dirt, or the like, it is possible to remove the clogging ofdirt, or the like to thereby drive the valve shaft again.

In the method of controlling an exhaust gas recirculation valveaccording to the invention further comprises the step of graduallydecreasing the driving current to the motor from a valve-openingposition exceeding a target position in a steady state so as to causethe open-close valve to move in the valve closing direction by thereturn torque until the valve-opening position closes to the targetposition.

Therefore, it is possible to open the valve to the target valve-openposition quickly and stably with a small amount of driving electriccurrent.

In the method of controlling an exhaust gas recirculation valveaccording to the invention further comprises the step of lowering adriving frequency for opening and closing a power feeding circuit to themotor if an ON-duty to open and close the power feeding circuit becomeslarger than a set value.

Therefore, when the valve shaft becomes difficult to move and thedriving power to the motor increases, the opening and closing frequencyof the power feeding circuit for the motor can be decreased previously.As a result, it is possible to prevent the damages to the switchingelement due to heat generation as well as the seizure of the motor.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a conventional schematic diagram showing an arrangement of acontrol valve as an EGR valve disposed in an exhaust gas recirculationpassage c which communicates an exhaust passage “a” of an exhaust engineE with an intake passage b.

FIG. 2 is a characteristic diagram showing the relationship between amotor torque and an opening and closing. position of a control valve inan EGR valve of torque balance drive system.

FIG. 3 is a characteristic diagram showing the relationship between thetime and the operating position of a motor shaft.

FIG. 4 is a longitudinal sectional view of the EGR valve.

FIG. 5 is a block diagram of an ECU apparatus for carrying out themethod of controlling the EGR valve in the so-called torque balancedriving system using a motor.

FIG. 6 is a block diagram showing a control part in the ECU.

FIG. 7 is a flow chart explaining the control method of the invention.

FIG. 8 is a subflow chart explaining a computation of the manipulatedvariable at step St1 in FIG. 7.

FIG. 9 is a subflow chart explaining an EGR control during faultcondition at step ST8 in FIG. 7.

FIG. 10 is a subflow chart explaining an EGR transistor duty output ofthe EGR transistor duty at step ST7 in FIG. 7.

BEST MODE FOR CARRYING OUT THE INVENTION

In order to describe this invention in more detail, the best mode forcarrying out the invention will be described with reference to theaccompanying drawings.

This invention is directed to a method of controlling an EGR valve of aunipolar drive construction in which a return torque is given by urgingmeans in one direction (in the valve closing direction) of an open-closevalve and a motor torque is given by a motor M in the other direction(in the valve opening direction) so that the open-close valve is openedto a target position by a torque balance between the both torque,comprising the step of stopping the power feeding to the motor M if theopen-close valve failed to operate despite a full (100%) continuouspower feeding to the motor M for a predetermined period of time or more.

The operation of the invention will now be described.

FIG. 7 is a flow chart explaining the control method of the invention.Incidentally, the internal processing at step ST1, step St7, and stepST8 will be shown below in FIGS. 8-10.

First, a manipulated variable is computed, i.e., a process duty (p-duty)is calculated (step ST1), and a judgement is made as to whether thismanipulated variable is saturated at a full (100%) power feeding (1.0)or at a non-power feeding (0.0) (step ST2). If YES, the number ofsaturation (e-count) is incremented by 1 (i.e., e-count+1) (step ST3),and further a judgement is made as to whether the time to be determinedby this number of saturation (e-count) has exceeded a predetermined full(100%) power feeding time (E-TIME-UP−1) (step ST4). If YES, the EGRcontrol during fault condition is executed (step ST8), otherwise theprocessing proceeds to step ST6.

At step ST2, if NO, the number of saturation (e-count) is zero (0)cleared (step ST5). Then, the calculated process duty (p-duty) is set toa transistor duty (tr-duty) for opening and closing a transistor(switching element) which opens and closes the power feeding circuit forthe motor M (step ST6), and an EGR transistor duty is outputted (stepST7). The RGR control during fault condition is performed at everyEGR-SAMPLE TIME.

Next, the computation of the manipulated variable, the EGR controlduring fault condition, and output of the EGR transistor duty performedat step ST1, step ST8, and step ST8 respectively in FIG. 7 will bedescribed.

FIG. 8 is a subflow chart explaining the computation of the manipulatedvariable at step ST1 in FIG. 7.

Function (x) is set to the target-position (step ST11), and the valvelift amount detected by the position sensor 40 to the current positionamount (real-position)(step ST12). The deviation (error-position) isobtained by the following formula (step S13)

(real-position)−(target-position).

Then, a difference (def-p-duty) of the manipulated variable is obtainedby the following formula (step ST14)

−(error-position)×I-GAIN (integrationconstant)−(error-position−old-error-position)×P-GAIN (proportionalconstant).

Thereafter, the deviation (error-position-) obtained by the abovecalculation is set to the previous deviation (old-error-position) (stepST15). A judgement on a steady state is made based on the deviationvalue (step ST16). If YES, the difference (d-p-duty) is zero (0) cleared(step ST17), otherwise the above process duty (p-duty) is increased byadding the difference (def-p-duty)(step ST18). In case of YES, thedeviation value is within a range of tolerance and is judged to be in asteady state.

A judgement is made as to whether the process duty (p-duty) is more thanthe full (100%) power feeding (1.0) (step ST19). If YES, the full (100%)power feeding (1.0) is set to the process duty (p-duty) (step ST20),otherwise, a judgement is made as to whether the process duty (p-duty)is less than the non-power feeding (0.0) (step ST21). If YES, thenon-power feeding (0.0) is set to the process duty (p-duty) (step St22)otherwise the computation of the manipulated variable is finished.

FIG. 9 is a subflow chart explaining the EGR control during faultcondition at step ST8 in FIG. 7.

First, a judgement is made as to whether the time to be determined bythe number of saturation (e-count) has exceeded the predetermined full(100%) power feeding time by three times (E-TIME-UP−3) or not (stepST31). If YES, the predetermined full (100%) power feeding time by threetimes (E-TIME-UP−3) is incremented by 1 (i.e., E-TIME-UP−3+1) and is setto the number of saturation (e-count) (step ST35), and the non-powerfeeding (0.0) is set to the transistor duty (tr-duty) (step ST36).

At step ST31, if NO, a judgement is made as to whether there is aremainder by dividing the predetermined full (100%) power feeding time(E-TINE-UP−2) by the time to be determined by the number of saturation(e-count) (step ST32). If there is a remainder (≠0), the process duty(p-duty) is set to the transistor duty (tr-duty)(step ST33), otherwise(=0) 1−process duty is set to the transistor duty (tr-duty), therebyreversing the direction of saturation, i.e., the rotation of the motor M(step ST34). After that, the operation of the EGR control during faultcondition is finished.

FIG. 10 is a subflow chart explaining the output of the EGR transistorduty at step ST7 in FIG. 7.

First, a judgement is made as to whether the transistor duty (tr-duty)is less than a judgement duty (HI-DUTY-RATE) which is a constantobtained in advance by through experiment or simulation (step ST41). IfYES, the base frequency (BASE-FREQUENCY) which is the fundamentalfrequency is set to a transistor frequency (tr-frequency) (step ST42),otherwise the resultant of the following formula is set to thetransistor frequency (tr-frequency) and the processing proceeds to stepST43 (step ST45)

BASE-FREQUENCY×(1−tr-duty)/(1−MOD-DUTY).

Then, the driving frequency of the EGR driving transistor is set to thetransistor frequency (tr-frequency) (step ST43), and the driving duty ofthe EGR driving transistor is set to the transistor duty (tr-duty) (stepST44). After that, the output of the EGR transistor duty is finished.

As mentioned above, according to the invention, if the open-close valvedoes not operate despite a full (100%) continuous power feeding to themotor for a predetermined period of time or more, the power feeding tothe motor is stopped. In this manner, even in case the valve shaftceases to move due to biting, clogging of dirt, or the like, it ispossible to prevent previously the occurrence of a seizure by anunnecessary power feeding.

In addition, if the open-close valve does not operate despite a full(100%) continuous power feeding to the motor for a predetermined periodof time or more, the motor is driven in the reverse direction andthereafter is driven in the forward direction. In this manner, thebiting, clogging of dirt, or the like is removed and the valve shaft isdriven again.

Further, in a steady state, the driving current to the motor isgradually decreased from a valve-opening position beyond a targetposition so as to cause the open-close valve to move in the valveclosing direction until the valve-opening position closes to the targetposition. Having been taken such an arrangement, it is possible tocoincide the valve-opening position with the target position quickly andstably with a small amount of driving current.

Still further, if an ON-duty for opening and closing the power feedingcircuit for the motor becomes larger than a set value, the drivingfrequency for opening and closing the power feeding circuit for themotor is lowered. Having been taken such an arrangement, when the valveshaft becomes difficult to move and accordingly the power fed to themotor increases, the number of opening and closing the power feedingcircuit for the motor can be reduced. As a result, it is possible toprevent previously the damage to the switching element due to heatgeneration and the seizure of the motor.

While In the above embodiment, a description was made about the PIcontrol, the invention may also be applied to the PID control as amatter off course because PID control belongs to the category of PIcontrol.

Industrial Applicability

As described above, the apparatus for controlling the exhaust gasrecirculation valve according to the invention is suitable for quicklyperforming the operation of partly recirculating the exhaust gas in theexhaust passage “a” to the intake passage “b” in response to the changein the operating conditions of the engine.

What is claimed is:
 1. A method of controlling an exhaust gasrecirculation valve wherein a valve-open position is controlled by atorque balance between a return torque given by urging means in thevalve closing direction and a motor torque given by a motor in the valveopening direction, comprising the step of stopping power feeding to saidmotor if an open-close valve failed to operate despite a full (100%)continuous power feeding to said motor for a predetermined period oftime or more.
 2. The method of controlling an exhaust gas recirculationvalve according to claim 1, further comprising the step of driving saidmotor in the valve closing direction and thereafter driving said motorin the valve opening direction again if said open-close valve failed tooperate despite a full (100%) continuous power feeding to said motor fora predetermined period of time or more.
 3. The method of controlling anexhaust gas recirculation valve according to claim 1, further comprisingthe step of gradually decreasing the driving current to said motor froma valve-opening position exceeding a target position in a steady stateso as to cause said open-close valve to move in the valve closingdirection by the return torque until said valve-opening position closesto the target position.
 4. The method of controlling an exhaust gasrecirculation valve according to claim 1, further comprising the step oflowering a driving frequency for opening and closing a power feedingcircuit for said motor if an ON-duty to open and close said powerfeeding circuit becomes larger than a set value.